In Code Division Multiple Access systems (CDMA), several users share the same frequency. Different users are separated from each other by codes. The use of the same frequency causes interference to other cells. The transmit power control is the most important parameter used to limit the interference, because the higher the power, the more interference. This is why the power control is the key issue especially in the CDMA systems.
There are, however, many problems in the power control. For instance, the calculation of the load factor or of the capacity utilisation need the estimation of the interference caused by other cells. The interference originating from neighbouring cells can be even 40 percent of the total interference in the cell. Attention also had to be paid to the fact that the downlink interference varies for every user of the cell mainly due to the variation of locations. Another fact which has to be taken into consideration is that the user equipment only knows the total interference. All these matters make the power control estimation and thereby power restriction difficult in the CDMA systems especially in multi-cell environments.